Effect of plasma niobizing on oxidation resistance of TiAl intermetallics

In the present paper, plasma niobizing has been performed on TiAl substrates and the oxidation behaviors were investigated. The compositions and microstructures of the surface alloyed layers as well as oxidation scales were investigated by means of X-ray diffraction, scanning electron microscopy, BSE, energy dispersive X-ray analysis and EPMA. The diffusion layers have formed on TiAl substrates in plasma niobizing process. Untreated TiAl and niobized TiAl specimens were oxidized in static air for 360 ks at 1223 and 1323 K. The results indicate that plasma niobizing remarkably improves the oxidation resistance of TiAl. The interrupted-oxidation kinetics curve of bare TiAl is approximately a straight line. In contrast, the mass of all the niobized specimens increase in accordance with logarithmic law. The oxidation rate of plasma niobized TiAl in steady stage decreases by more than one order of magnitude. The roles of plasma niobizing for improving the oxidation resistance are discussed by consideration of the structural changes induced by the plasma niobizing.